This invention relates to electroplating cells, and is more particularly directed to an injection or sparger means which provides an even flow of electrolyte onto and across the substrate to be plated.
Electroplating plays a significant role in the production of many rather sophisticated technology products, such as masters and stampers for use in producing digital compact discs or CDs. However, as these products have become more and more sophisticated, the tolerances of the plating process have become narrower and narrower. For example, in a modem CD, any impurities or blemishes of one micron or larger can create unacceptable data losses. Current electroplating techniques can result in block error rates of 70, and with higher density recordings, the block error rate can be 90 or higher. Current plans to increase the data density of compact discs are being thwarted by the inability of plating techniques to control blemishes in the plating process.
A number of techniques for electro-depositing or coating on an article face been described in the patent literature, but none of these is able to achieve the high plating purity and evenness of application that are required for super-high density compact discs.
Andros et at. U.S. Pat. No. 4,376,031 describes electrophoretic coating apparatus in which a suspension of electrophoretic material is contained in a tank. In this apparatus a distribution manifold has a pair of discharge robes provided with a series of orifices to create a non-turbulent flow of the suspension.
Santini U.S. Pat. No. 4,696,729 is directed to an electroplating cell which has a channel formed between wall members to create an even, non-turbulent flow of the plating solution. In this scheme, the electrolyte passes through an isostatic chamber containing small spherical glass beads that are held in place by a screen-like membrane. The flow of the solution is in the direction across the surface of the workpiece.
Turner U.S. Pat. No. 4,062,755 relates to a sparging system for an electroplating cell, in which a plating chamber has a perforated partition, i.e. , with a series of slots, to create an upward flow of the plating solution.
Glenn U.S. Pat. No. 3,963,588 shows a slotted sparger for a high current density electroplating process. The sparger can have an elongated discharge port.
Lowe U.S. Pat. No. 2,181,490 relates to an electroplating set-up that employs elongated injection nozzles for distributing electrolyte to a circular substrate or workpiece.
Johnston U.S. Pat. No. 4,435,266 is directed to an electroplating arrangement for making stamper plates, with an injection tube that flows the electrolyte axially against the plated face of the substrate.
Faulkner U.S. Pat. No. 3,634,047 describes an electroplating technique, where a cone head is employed to maintain the velocity head of electrolyte that is pumped through a baffle box into the plating tank. The cone head member has two groups of outlet ports, with the ports being of progressively changing diameters, and an arrangement of baffle members are intended to create a constant pressure of the plating solution that flows across the workpiece.
Shibata U.S. Pat. No. 3,400,067 is directed to an electrolytic cell that has a guide slit for discharge of mercury at a uniform flow rate. This is achieved with a pattern of profiled holes which can be variable in geometry.
Ransey et al. U.S. Pat. No. 3,450,625 concerns an electroplating technique in which a foraminous screen separates a tank into anode and cathode compartments. The screen is typically metal cloth or fabric. Sludge accumulates in an accumulator behind the screen.
Thurber U.S. Pat. No. 2,487,399 concerns an electroplating apparatus in which there are separate anodic and cathodic cells separated by membranes. The apparatus includes anodic filtering and circulating. Three cells are involved, including a plating tank and two separate overflow tanks.
Holsinger U.S. Pat. No. 3,788,965 describes a set-up for refining metal ore by selective electroplating from a solution of the ore. An acid solution of the ore is separated from a basic solution by means of an inert permeable barrier.
None of these prior plating arrangements employed a laminar flow sparger or injection nozzle within the plating bath, and none of these has achieved even, laminar flow across the face of the substrate during the plating operation. None of these plating cells or baths have employed a backwash technique that carries the sludge and particulate impurities away from the article to be plated, and none of these techniques has been capable of producing a flat plated article of high tolerance, such as a high-density compact disc master or stamper.
In the manufacture of compact discs, there is a step that involves the use of a so-called stamper. The stampers are negative discs that are pressed against the material for the final discs to create an impression that becomes the pattern of tracks in the product compact discs.
Stampers are nickel and are electroformed. The stampers are deposited on a substrate that has the data tracks formed on it, and has been provided with a conductive surface, e.g., by sputter coating. Then the substrate is placed into a plating tank. The nickel is introduced in solution into the process cell so that it can be electrochemically adhered onto the substrate surface, using standard electroplating principles. Present industry standards require the stamper to have an extremely high degree of flatness, and where higher density storage is to be achieved, the flatness tolerance for the nickel coating becomes narrower and narrower.
The flow regime for the plating solution within the tank or cell is crucial for successful operation. Flow regime is affected by such factors as tank design, fluid movement within the process vessel, distribution of fluid within the vessel and at the zone of introduction of the solution into the vessel, and the uniformity of flow of the fluid as it is contacts and flows across the substrate in the plating cell.
Present day electroplating cells employ a simple technique to inject fluid into the process vessel or cell. Usually, a simple pipe or tube is used with an open end that supplies the solution into the tank or cell. The solution is forced from the open end of the pipe. This technique is not conducive to producing a flat coating, due to the fact that the liquid is not uniformly distributed across the surface of the workpiece. This technique can create high points and low points in the resulting plated layer, because of localized eddies and turbulences in the flow regime.
Other problems frequently arise from the presence of impurities that are included within the anode material. That is, the lumps or nuggets of nickel that are contained in the anode typically contain some oxides and other impurities. As the nickel material is consumed, impurities accumulate as sludge within the anode chamber. During the plating process, particles of the sludge tend to migrate to the cathode side and can contaminate the plating on the substrate. Typically the anode material is contained in a cloth anode bag which is intended to hold the sludge as the material is consumed. However, the bag is unable to contain particles of micron size, which can damage the tracks of the CD stamper.